The present invention relates to a magnetic recording medium. More particularly, it relates to a coated magnetic recording medium, such as a magnetic recording tape, including a magnetic upper layer coated on to a lower support layer, and methods of manufacturing the same.
Magnetic recording media, such as magnetic recording tapes, have continually evolved to satisfy the seemingly endless need for increased recording density or capacity per unit volume. In general terms, magnetic recording media generally comprise a magnetic layer coated onto at least one side of a non-magnetic substrate (e.g., a film for magnetic recording tape applications). With certain designs, the magnetic coating (or xe2x80x9cfront coatingxe2x80x9d) is formed as a single layer. In an effort to reduce a thickness of this magnetic recording layer, a more recent approach is to form the front coating as a dual layer construction, including a support layer (or xe2x80x9clower layerxe2x80x9d) on the substrate and a reduced-thickness magnetic layer (or xe2x80x9cupper layerxe2x80x9d) formed directly on the support or lower layer. With this construction, the lower layer is typically non-magnetic or substantially non-magnetic, generally comprised of a non-magnetic powder and a binder. Conversely, the upper layer comprises a magnetic metal particle powder or pigment dispersed in a polymeric binder. Finally, with magnetic recording tape, a backside coating is applied to the other side of the non-magnetic substrate in order to improve the durability, conductivity, and tracking characteristics of the media.
As might be expected, the formulation intricacies associated with the requisite upper layer, lower layer, and back coat, as well as coating of the same to an appropriate substrate, are highly complex, and vary from manufacturer to manufacturer. That is to say, the numerous chemistry and processing variables attendant with dual layer (i.e., upper layer and lower layer, as described above) magnetic recording media invariably result in each magnetic recording media manufacturer having different layer formulations and processing techniques.
Notwithstanding the inherent component and processing variations, certain base materials are commonly employed with many magnetic recording media, including magnetic recording tapes. To this end, magnetic tapes from two different tape manufacturers will often employ several of the same components in one or more of the upper layer, lower layer and back coat. Thus, any improvements to these common material types, amounts or performance characteristics can be universally beneficial. For example, conductive carbon black is typically used as the lower layer conductivity component. Unfortunately, the amount of conductive carbon black normally required to provide requisite conductivity can negatively affect rheology and dispersion quality of the overall lower layer coating.
The conductive carbon black concern described above is but one example of macro-level issues faced by many magnetic recording media manufactures. With reference to specific magnetic recording tape formats, a multitude of other, more exacting formulation and processing issues must be addressed. Thus, a need exists for a magnetic recording medium that exceeds performance requirements and entails broadly applicable improvements.
One aspect of the present invention relates to a magnetic recording medium including a non-magnetic substrate, a back coat, a lower support layer, and a magnetic upper layer. The substrate defines a front side and back side, with the back coat being formed on the back side. The lower layer is disposed over the front side of the substrate and includes a primary powder material and a conductive carbon black material dispersed in a binder. The lower layer primary powder material consists of particles having a coercivity in the range of 0-300 Oe coated with an electroconductive material. Amounts of the electroconductive coating material and the conductive carbon black are provided based upon the following relationship between a weight percent of the conductive carbon black and a weight percent of the electroconductive coating:
14xe2x88x922xxe2x89xa6yxe2x89xa630xe2x88x92x, and
8xe2x89xa6y, and
0.5xe2x89xa6xxe2x89xa613, where
x=weight percent of conductive carbon black in the lower layer formulation; and
y=weight percent of the electroconductive coating material in the lower layer formulation.
The magnetic upper layer is disposed over the lower layer and includes a magnetic powder dispersed in a binder. In one preferred embodiment, the lower layer primary powder is carbon-coated hematite, and a weight ratio of the coated hematite to the conductive carbon black material is 1.5 to 3.5 parts by weight conductive carbon black, based upon 100 parts by weight of the carbon-coated hematite (1.5% to 3.5% conductive carbon black based on weight of the carbon-coated hematite). In another preferred embodiment, the lower layer and upper layer formulations include a stearic acid lubricant that is more than 90 percent pure.
Another aspect of the present invention relates to a magnetic recording medium including a non-magnetic substrate, a back coat, a lower support layer, and a magnetic upper layer. The substrate defines a front side and back side, with the back coat being formed on the back side. The lower layer is disposed over the front side of the substrate and includes a primary powder material and a conductive carbon black material dispersed in a binder. The lower layer primary powder material consists of particles having a coercivity of less than 300 Oe coated with an electroconductive material. With this in mind, the conductive carbon black is provided in an amount of 1 to 5 parts by weight based upon 100 parts by weight of the primary powder material. The magnetic upper layer is disposed over the lower layer and includes a magnetic powder dispersed in a binder.
Yet another aspect of the present invention provides a method for producing a coated magnetic recording medium. The process includes applying a lower layer coating material onto a front side of an elongated, non-magnetic substrate strip. An upper layer coating is then applied onto the coated lower layer coating material. The upper layer and lower layer coating materials are dried to form a medium including a lower support layer and an upper magnetic layer on the substrate. The medium is wound and stored in a below ambient temperature environment. Following cooled storage, the wound medium is calendered.